1. Field of the Invention
This invention relates to a seal plate drive assembly and, more specifically, to a seal plate drive assembly for use with apparatus for pressure cooking a farinaceous product. In particular, the present invention relates to a seal plate drive assembly for use with apparatus for pressure feeding and pressure cooking a food product and, in which, the apparatus includes a pressure feeder assembly, a seal plate and seal plate drive assembly for compacting and regulating the flow of product mix in a terminal portion of the pressure feeder assembly and a pressure cooker assembly. Additionally, the apparatus for which the invention is primarily intended also includes an extruder assembly for extruding the pressure cooked food product and a cut-off assembly for pelletizing the extruded product.
2. Description of the Prior Art
The present invention is an improvement over applicant's assignee's cooker/extruder apparatus which is fully disclosed in U.S. Pat. No. 3,246,594 to C. D. Fisher, the disclosure of which is intended to be incorporated herein by reference.
Briefly, disclosed in the aforesaid U.S. Pat. No. 3,246,594 is an apparatus for continuously pressure cooking various cereal materials, under superatmospheric steam conditions, to produce a cooked, extrudable mash and, then, extruding the cooked mash through a plurality of die orifices. An important requisite for the successful operation of this apparatus is the ability to form a pressure resistant seal at the inlet to the pressure cooker. In accordance with the patent, this seal is created by compacting the dry incoming material or particulate product mix into a pressure resistant plug in the outlet or terminal end of its pressure feeder mechanism. Further, in accordance with the patent, after the seal has been formed, it is generally then desirable or necessary to abrade the compacted material back to its original particulate state to assure uniform and thorough penetration of the superatmospheric steam in the pressure cooker. A suitable mechanism and procedure for accomplishing the seal/abrasion function is fully disclosed in the patent.
More specifically, in accordance with the above-mentioned patent, dry incoming material is advanced from a materials inlet or hopper to the pressure cooker inlet by a pressure feeder mechanism consisting of a screw conveyor. As the material advances from the inlet of the screw conveyor to its discharge or terminal end, partial compaction of the material occurs as a result of a decrease in the flight channel depth of the feeder screw, created by increasing the root diameter of the screw. Further compaction occurs as the material advances against a rotatable and axially translatable seal plate or gate disposed in confronting relation to the outlet end of the screw conveyor. The seal plate or gate is mounted on a shaft extending through or into a feeder housing connecting the screw conveyor discharge to the pressure cooker inlet. The force with which the seal plate is held against the advancing material, as well as its axial movement, is controlled by a fluid actuated, piston-cylinder assembly connected to the distal end of the seal plate shaft. The abrasion function is accomplished by rotating the seal plate shaft and, accordingly, the seal plate and associated abrading lugs through a jack-shaft/gear drive arrangement. During normal operation, simultaneous axial movement and rotation of the seal plate shaft will continuously take place. Since the apparatus is operating against superatmospheric steam pressure, it is necessary to provide a shaft seal. The shaft seal disclosed in the patent is a packing gland arrangement.
While the above-described assembly functions satisfactorily, it does have certain drawbacks. First, the packing gland, by design, must have a slight clearance between the rotating shaft and the packing. Consequently, there will be leakage of superatmospheric steam, as well as the materials being processed. If the clearance is too great, leakage will be excessive and will create a massive buildup of raw materials in the housing surrounding the seal plate drive assembly. If there is no clearance, the packing will run dry creating frictional heat and causing degradation of the packing gland. Running dry can also cause the shaft to be scored and excessive leakage to begin. Additionally, because of the axial movement of the shaft, process materials, some of which are highly abrasive, can be drawn along with the shaft into the packing gland. Proper maintenance and adjustment of the packing glands depends upon the skill, judgment and attention of the operator. Second, support of the drive shaft is difficult. The drive shaft bearings must permit both axial and rotational movement. The bearings and/or bushings disclosed in the patent are generally satisfactory but their life is limited. Finally, because of the axial movement of the shaft, the drive gears must slide on each other. As the gears wear, problems can be experienced with smooth, uniform axial movement. It is the correction or elimination of the foregoing limitations or deficiencies of the prior art to which the present invention is directed.